CVE.org (no NVD analysis yet)· CNA GitHub_M

CVE-2026-125111: Rack: Multipart parsing allows DoS via unbounded scan buffer growth

HighCVSS 7.5 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 30/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.36% (FIRST EPSS).
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: ruby-rack (Debian:14) 3.2.8-1; rack (RubyGems) 3.1.23, 3.2.8, 2.2.25.

Low priority for now. Upgrade to ruby-rack (Debian:14) 3.2.8-1; rack (RubyGems) 3.1.23, 3.2.8, 2.2.25 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

Rack is a modular Ruby web server interface. Prior to 2.2.25, 3.1.23, and 3.2.8, Rack::Multipart::Parser can retain parsed data in its internal StringScanner buffer when reads end inside or immediately after multipart headers. An unauthenticated attacker can align many small parts with rack.multipart.buffer_size boundaries so the buffer grows with the request despite per-field, header, and preamble limits, causing a worker to exhaust memory. The attack requires only a well-formed multipart body and affects applications that parse multipart requests. This issue is fixed in versions 2.2.25, 3.1.23, and 3.2.8.

Published: Nov 9, 2026
Updated: Nov 12, 2026
EPSS: 0.3% · 30th percentile
CWE: CWE-400

Report tools

JSON

Action score

Monitor

Low priority for now.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.3%

CISA SSVC decision

Exploitation: none
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: —
CNA · GitHub_M: 7.5; NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

rack rack
- < 2.2.25, >= 3.0, < 3.1.23, >= 3.2, < 3.2.8affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	ruby-rack	from 0	—
Debian:14	ruby-rack	before 3.2.8-1	3.2.8-1
RubyGems	rack	from 3.0.0 · before 3.1.23	3.1.23
RubyGems	rack	from 3.2.0 · before 3.2.8	3.2.8
RubyGems	rack	before 2.2.25	2.2.25

Same product

rack: all records

Other highest-scoring records for the same primary product.

CVE-2024-25126Rack ReDos in content type parsing (2nd degree polynomial)
41Plan
CVE-2024-26146Possible Denial of Service Vulnerability in Rack Header Parsing
31Monitor
CVE-2023-27530A DoS vulnerability exists in Rack <v3.0.4.2, <v2.2.6.3, <v2.1.4.3 and <v2.0.9.3 within in the Multipart MIME parsing code in which could…
31Monitor

Published before and after this one in the same product

← EarlierCVE-2026-125108Nov 9, 2026 · Rack: Multipart boundary ambiguity guard in Rack::Multipart::Parser can be bypassed with a quoted boundary value, allowing WAF bypass
14Monitor
← EarlierCVE-2026-125109Nov 9, 2026 · Rack: Rack::Request#host_with_port (and #base_url / #url) return the raw invalid Host header — incomplete fix of CVE-2026-34835
19Monitor
← EarlierCVE-2026-125110Nov 9, 2026 · Rack: Rack::Static header_rules bypass via dot-segment normalization mismatch
21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
debian:ruby-rack	3.2.8-1 · Debian:14	Package registry (OSV)
RubyGems:rack	2.2.25	Package registry (OSV)
RubyGems:rack	3.1.23	Package registry (OSV)
RubyGems:rack	3.2.8	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

PublishedNov 9, 2026
Fix recordedNov 10, 2026+1 d
TodayNov 13, 2026+4 d

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

CVE-2026-34230221 days apartRack: Quadratic complexity in Rack::Utils.select_best_encoding via wildcard Accept-Encoding header
30Monitor
CVE-2026-34826221 days apartRack: Unbounded Range Count in get_byte_ranges Enables DoS
30Monitor
CVE-2026-34827221 days apartRack: Algorithmic-Complexity DoS in Rack::Multipart::Parser
30Monitor
CVE-2026-34829221 days apartRack: Denial of Service via Unbounded Multipart File Upload Without Content-Length
30Monitor
CVE-2025-61919395 days apartRack is vulnerable to a memory-exhaustion DoS through unbounded URL-encoded body parsing
30Monitor
CVE-2025-61771398 days apartRack's multipart parser buffers large non‑file fields entirely in memory, enabling DoS (memory exhaustion)
30Monitor

Not on record for this CVE: researcher credit · public bounty program.

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-secondary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

SSVC exploitation— → noneNov 12, 2026, 8:07 PM UTC
Fix✗ → ✓Nov 10, 2026, 9:07 PM UTC
Exploit maturity— → noneNov 10, 2026, 12:07 AM UTC

For records you follow, these changes also arrive as notifications. →

References

github.com/rack/rack/commit/244e75a840cee0823f86d5d01dc374505a8abed8

Show all references (3 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

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